Conventionally, in a television broadcasting station etc., use has been made of a transmitting apparatus of a serial digital interface (SDI) system defined as SMPTE-259M in the SMPTE (Society of Motion Picture and Television Engineering) as the infrastructure for performing the transmission of audio and video data of the digital format. Further, also a serial digital data interface (SDDI) which improves upon the SDI system while maintaining compatibility and enables the transmission of variable length data and a plurality of types of data by a single transmission packet has been proposed.
Further, recently, an asynchronous transmission mode (ATM) system has been put into practical use as a high speed digital data transmission system.
There is demand for audio and video data to be sent and received (transmitted) via an ATM communication line between television broadcasting stations by the SDI system or the SDDI system. However, the transmission packet of the above SDI system has a one-word 10-bit configuration while the ATM cell used in a communication line of the ATM system has a one-word eight-bit configuration. Accordingly, the transmission packet of the SDI system can not be used for an ATM communication line as it is.
Further, in television broadcasting stations etc., there are cases where the transmitted audio and video data should be telecast in real time. In such cases, there arises a problem of the transmission delay time produced in the communication line. That is, if the transmitted audio and video data is telecast as it is by using a synchronization signal on the reception side, there arises an inconvenience that the video is interrupted at the boundaries of the video images. In order to eliminate such an inconvenience, transmission compensating for the transmission delay time between transmission apparatuses can be considered.
In order to perform transmission while compensating for the transmission delay time, it is necessary to measure the transmission delay time. As a method for measurement of the transmission delay time, for example, there can be considered a method wherein one transmitting apparatus is regarded as a master, another transmitting apparatus is regarded as a slave, the data transmitted from the master side is returned at the slave side, and the time difference between the transmitted data and the returned data is detected. According to this method, however, because of the content of the processing at the transmitting apparatus on the master side and the content of the processing at the transmitting apparatus on the slave side, the processing is troublesome. In addition, measurement of the transmission delay time among three or more transmitting apparatuses connected to the communication line is difficult.